Spectrophotometers are commonly used in many industries to measure intensity as a function of the color, or more specifically, the wavelength of light. Typically, a spectrophotometer illuminates a specimen (which is either reflecting or transmitting) with a calibrated light source, and then measures the reflected light in order to characterize the specimen's reflectance spectrum.
Conventional spectrophotometers employ a pulsed xenon light source to illuminate specimens. While such light sources tend to be fairly reliable when properly maintained and filtered, they are also associated with many drawbacks. For instance, pulsed xenon light sources tend to be difficult to handle, physically, because they are relatively large, they produce dangerous voltages, they become very hot in use and they are electronically noisy. From a technical standpoint, they also tend to be slow (e.g., due to re-charging of capacitors after triggering), unstable (e.g., the plasma is geometrically unstable, making it difficult to couple energy into fiber optics easily), variable (e.g., different spectral power distributions may be produced from flash to flash), subject to inaccurate filtering (e.g., tends not to match required spectral power distributions) and difficult to couple closely with optics (e.g., due to extremely high pulsed energies). Moreover, the equipment is expensive, as is the filtering required to achieve many desired spectra of illumination. All of these drawbacks are associated with equipment that generally tends to have a short lifetime.
Some spectrophotometers have incorporated light emitting diode (LED) light sources in order to address some shortcomings associated with pulsed xenon light sources. In such configurations, however, each LED comprising the light source is capable of producing only one spectral measurement, since LED types are conventionally turned “on” one by one. Moreover, the characterization of a specimen's reflectance spectrum may be skewed by the transmittal of the LEDs' spectra (which are typically subject to complicated changes when their intensities are varied) to an analyzing device.
Thus, there is a need in the art for an improved spectrophotometer with an LED illuminator that allows for more precise measurement and characterization of a specimen's reflectance spectrum.